function df=dfun(x)
df=[1,10,0,0;
    0,0,sqrt(5),-sqrt(5);
    0,2*(x(2)-2*x(3)),2*(x(2)-2*x(3))*(-2),0;
    2*sqrt(10)*(x(1)-x(4)),0,0,-2*sqrt(10)*(x(1)-x(4))];
end